Electron discharge tube



March 15, 1966 F. G. A. HAEGELE ELECTRON DICHARGE TUBE 2 Sheets-Sheet 1 Filed Oct. 15, 1963 F/GS.

Inventor FEEDER/(k G. A, H E HE Attorney March 15, 1966 F. G. A. HAEGELE ELECTRON DICHARGE TUBE 2 Sheets-Sheet 2 Filed Oct. 15, 1963 Inventor REDERICK G. A. HAEGElE 7 Attorney United States Patent 3,240,981 ELECTRON DISCHARGE TUBE Frederick Gustav Adolf Haegele, London, England, as-

Signor to international Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 15, 1963, Ser. No. 316,302 7 Claims. (Cl. 313-350) The present invention relates to thermionic valves incorporating frame grids and is particularly concerned with the construction of such grids and of electrode structures using them.

A frame grid, as the term is used in the present specification and claims, is a grid wound on a frame formed by two parallel side rods secured rigidly together at each end by spacing means such as metal straps. In the window so formed a helical winding of very fine wire is wound under tension sufficient to maintain the turns of the wire in position during processing and use of the valve, the Wire being wound around the side rods and, in normal practice, bonded to the side rods by glazing or gold soldering. In the conventional frame grid, the form of which is illustrated in FIG. 1 of the accompanying drawings, at each end of the winding (not shown) a pair of ribbon-shaped metal straps 2 are welded to the respective side rods 1. Commonly the side rods and straps are of the same material, say molybdenum, and the grid wire is tungsten. In a typical example such a frame gn'd would have 100 turns of 0.0003 inch tungsten wire wound at 380 turns per inch at 6 grams tension over two parallel molybdenum side rods each 0.0325 inch in diameter. The resultant tension between the side rods is consequently substantial, so that comparatively thick Straps are needed to maintain the structure rigid. Thus, for the example quoted above, each of the molybdenum straps would be made from 0.008 inch by 0.020 inch strip.

To a large extent the detailed form of electrodes in a frame grid electrode structure is determined by the method of assembly it is desired to adopt in building up the complete structure. In general, a frame grid electrode structure will include a central cathode, one or more grids surrounding the cathode, at least the control grid being a frame grid, and an anode surrounding the outermost grid. The cathode is normally in the form of a rectangular metal tube containing a heater and coated externally with electron emissive material. Each of the grids and the anode is tubular, having a transverse contour intermediate the rectangular and elliptical forms with well defined major and minor axes, the active portions of the electrodes being substantially planar. The major dimension of the electrode structure is parallel [to the longi tudinal axis and the structure is symmetrical with respect to this axis. In the assembly of a frame grid electrode structure such as discussed above, the grid or grids and the anode are secured between insulating bridges, usually mica, located parallel to one another by means of support rods which may be independent of the individual electrodes. Although it is possible to make electrodes in two parts which will lie on opposite sides of the plane containing the longitudinal axis and the major transverse axis of the electrode structure and subsequently to join them togetherthough joining may not always be necessaryit is more usual and convenient to make the electrodes tubular and to assemble them by passing one over the other. Because of operations involving gold-soldering, welding, or the like, it is not practical to wind the control grid with the cathode in place between the grid side rods; the structure must be such as to allow for insertion of the cathode into the completed grid. For this reason, in the conventional frame grid the straps are on ICE the outside of the side rods. Similarly, straps on a frame screen grid surrounding the control grid are also positioned on the outside of its frame to allow for assembly of the two grids, one within the other.

Because of the straps on the outside of the frame, no co-acting surrounding electrode, such as a further grid 0r anode, can normally be positioned closer to the grid winding than the thickness of the strap-0.008 inch in the example given above-plus any clearance necessary for insulation reasons.

It has previously been proposed, in a frame grid electrode structure, to replace the conventional pair of straps at one end of the grid by a single bridge-like spacer member whose thickness does not exceed that of the side rods. This arrangement allows such a frame grid to be closely surrounded by a further electrode without encountering the limitation imposed by the thickness of the conven tional straps. At the other end of the frame grid the usual strap-s were provided, so allowing the grid to be placed about a cathode. Provision had then to be made for locating the cathode and grid with respect to one another and to the remainder of the electrode structure. At the open end of the frame grid (the end having the external straps), a conventional mica insulator could be used, apertured to receive the cathode and the grid side rods. At the end of the frame grid closed by the bridgelike spacer member it was proposed to use an insulator engaging the said further electrode and having a generally rectangular aperture to receive the frame grid side rods and to allow passage, during assembly, for the bridgelike spacer member.

With the above described prior art arrangement additional means were required for locating the cathode at the closed end of the frame grid, for the side rods being necessarily thicker than the cathode, the rectangular aperture in the insulator above mentioned provided clearance between the insulator and the cathode.

It is an object of the present invention to provide an electrode assembly wherein a frame control grid surrounds a cathode and a further electrode closely surrounds the control grid and these electrodes are located with respect to one another by a single insulator at each end of the cathode.

It is a further object of the invention to provide aclose-spaced electrode assembly including a cathode, a surrounding frame control grid and a further electrode closely surrounding the control grid wherein the interelectode capacitances are kept as low as possible by the avoidance of additional dielectric material in the vicinity of the electrodes.

A further object of the invention is -to reduce interelectrode capacitances in an electron discharge device employing one or more frame grids coaxially surrounding a cathode by a novel shaping and disposition of the frame grid side rod spacing members.

In the present invention, at one end of the frame control grid the conventional side rod spacing straps are replaced by a single ribbon-shaped strut, of thickness no greater than that of the cathode, lying wholly between the planes of the grid wires, while, at this end of the cathode, a one-piece insulator is provided, apertured to receive the control grid side rods and arranged for securing to a further electrode closely surrounding the control grid, the insulator providing means for locating the cathode by being apertured also to receive an end of the cathode, the control grid side rod apertures and the cathode aperture being joined together by slots of narrower Width than the thickness of the cathode to allow passage during assembly for the said ribbon-shaped strut without impairment of the cathode locating means.

Other and further objects and features of the invention will become apparent from the following description of an embodiment of the invention made with reference to the accompanying drawings in which:

An embodiment of the invention will be described with reference to the accompanying drawings, in which:

FIG. 1 already referred to, shows a conventional grid frame;

FIG. 2 shows a frame grid used in the invention;

FIG. 3 shows an alternative means for securing together the frame grid side rods at one end in embodiments of the invention;

FIG. 4 illustrates an insulator according to the invention;

FIGS. 5, 6 and 7 are, respectively, perspective, longitudinal sectional, and transverse sectional diagrammatic views of an electrode structure according to the invention, FIG. 6 showing the complete valve assembly.

In the frame grid of FIG. 2 the side rods 1 are spaced apart at their upper ends by means of a ribbon-shaped strut 3 oriented with its wide sides parallel to the side rods. The strut may be morticed into the side rods at each end, or may simply be butt-joined thereto. The thickness of the strut is not greater than that of the cathode which the grid is to surround and the strut is positioned centrally between the pair of planes defined by the grid winding 4 so that no portion of the side rod spacing means projects beyond the winding in the direction of its mino axis. Thus the side rod spacing means at this end persents no obstruction to a close fitting further electrode being passed over the top of the grid into position about the winding 4. Abutments which may each be in the form of a ring of wire soldered to the required side rod, are placed at the upper end of the winding to locate the frame in mica bridge pieces. These rings, although stouter than the wire winding 4, do not project normal to the minor axis of the grid to anything like the extent of the external grid straps 2 of FIG. 1, but, if desired, alternative forms of abutment, not projecting along the minor axis of the grid, may be used.

At the lower end of the grid of FIG. 2, the side rod spacing means is a conventional pair of straps 2 as in FIG. 1, to allow for insertion of a cathode in between them.

Provided at one end of the frame the side rod spacing means does not obstruct entry of the cathode along the longitudinal axis of the grid, the invention allows for the use, at one end of the grid, of different side rod spacing means to those shown in FIGS. 1 and 2.

In FIG. 3 a single strap 8 is shown which is bent to project out from the plane of the grid wires so as to provide clearance for other electrode parts. The strap 8, which is ribbon-shaped, with the width of the ribbon in the direction of the longitudinal axis of the grid, would need to be somewhat more substantial than one of the straps 2 of FIG. 1.

An insulator for use in embodiments of the invention is illustrated in FIG. 4. A central aperture 10 accommodates a rectangular cathode and circular apertures 11 accommodate the side rods of a surrounding frame grid. The apertures 10 and 11 are joined together by slots 12 narrower than the thickness of the cathode, which allow passage therethrough of the strut 3 of FIG. 2. End apertures 13 of larger diameter afford means for securing the bridge piece to a pair of support rods.

The aperture 10 should provide a close fit about the cathode so as to prevent movement of the end of the cathode along either of the transverse axes of the grid. In order that the strut 3 of FIG. 2 may pass through the slots 12, the strut should be no thicker than the cathode and preferably thinner. If the insulator is of mica, the strut may be slightly thicker than the 'width of the slots, passage being permitted by the resilience of the material of the insulator.

In the valve embodiment illustrated in FIGS. 5, 6 and 7 a screen grid electrode construction is shown, the anode being omitted in FIG. 5. The section in FIG. 6 is taken along VI-VI on FIG. 5 and that of FIG. 7 along VII-VII on FIG. 6. A rectangular cathode 14 is surrounded by a control grid 15, a screen grid 16 and an anode 17. The electrodes are located by means of two mica bridge pieces 18, of which only part of one similar to that of FIG. 4, is shown in FIG. 5, secured to support rods 19 which also carry between them mica spacing members 20 and 21 which locate the electrode structure with respect to a surrounding glass envelope 22. The envelope carries a set of pins 23 sealed through its base in conventional manner and joined to the respective electrodes by leads such as 24. The grid 15 is of the form described above with reference to FIG. 2. The straps 2 seat on the lower bridge piece 18 while the upper ends of the side rods 1 pass through the upper bridge piece, longitudinal movement of the grid being restrained by the abutments 5 together with the straps 2. The screen grid 16, also a frame grid, closely surrounds the control grid. At the upper end of the screen grid the side rods 25 are secured together by means of a pair of straps 26 generally similar to the straps 2 but cut away as indicated at 27, FIG. 5, to increase the insulation resistance of the structure across the mica bridge piece. At the lower end a pair of straps 8, each similar to that of FIG. 3 is used. As they are bent away from the plane of the grid 'wires clearance is provided for the adjacent straps 2 of the control grid.

In building up the electrode assembly of FIGS. 5 to 7, the cathode is first inserted into the lower bridge piece 18, the control grid is slid over it and located in the piece 18. The screen grid can now be lowered over the control grid and the upper bridge fitted into position, the slots 12, FIG. 4, permitting passage over the strut 3. It will be observed, particularly from FIG. 7, that the planes of the winding of grid 16 intersect the thickness of the straps 2 of the control grid, i.e. the active portions of the screen and control grids are closer together than the thickness of a grid strap.

In a typical practical embodiment of the invention the minor axis of the control grid winding is 0.063 inch, providing a spacing between this winding and the cathode surface of 0.003 inch. The grid is wound at 350 turns per inch with wire 0.0004 inch in diameter. The minor axis of the frame grid is 0.077 inch, providing a spacing between the turns of the control and screen grids of 0.007 inch (less than the minimum thickness, 0.008 inch, which would be required to accommodate a strap of the conventional frame grid of FIG. 1). This close spacing has made it possible to design a valve in which the screen grid voltage is only 50 v. with respect to the cathode instead of the value of l00 v. which is required with a similar valve whose minimum spacing is limited by the construction of the frame grid of FIG. 1. Furthermore, since in embodiments of the invention the amount of dielectric material between the several electrodes is reduced to a minimum by the use of a single insulator at each end of the cathode, while the use of the ribbon-shaped strut of the frame grid allows the side rods supporting means to be further removed from adjacent electrodes, the interelectrode capacitances of the discharge device may be reduced to compensate for the increase brought about by the close spacing of the frame grid and the surrounding electrode.

It will be evident that the principles of the invention as described with reference to a screen grid valve embodiment are applicable also to cases where it is desired to reduce the spacing between a frame control grid and a surrounding anode.

It is to be understood that the following description of specific examples of this invention is not to be considered as a limitation on its scope.

What I claim is:

1. An electron discharge tube having a cathode, a frame control grid surrounding the cathode and at least one further electrode surrounding the control grid, the control grid having a pair of side rods, the ends of said rods extending beyond the end of said cathode, a winding of fine wire, under tension, wound about the side rods in two planes extending between and along said rods and spacing means for the side rods at each end of the winding; and an insulator at each end of the grid winding providing means for locating the cathode, the control grid and the further electrode with respect to one another; wherein, at one end of the control grid, the side rod spacing means includes a straight fiat ribbon-shaped strut, said strut being positioned between said end of said cathode and said ends of said rods and of thickness not greater than that of the cathode, the entire strut extending straight across from the surface of one rod to the surface of the other rod wholly within the planes of the grid wires, and wherein, the said insulator at one end of the control grid is apertured to receive the cathode and the side rods of the control grid and is adapted to be secured to the said further electrode, and slots, narrower in width than the thickness of the cathode, joining together the apertures for the cathode and the said side rods; the arrangement being such that, during assembly, the said slots afford passage for the said strut.

2. An electron discharge device as claimed in claim 1 wherein the ribbon-shaped strut has each of its ends morticed into the side rods.

3. An electron discharge device as claimed in claim 1 wherein, at the other end of the grid winding, the side rod supporting means comprises a pair of ribbon-shaped struts, one on each side of the frame.

4. An electron discharge device as claimed in claim 1 wherein abutment means are provided on the side rods at the end of the grid winding adjacent said strut to form seating for the said insulator.

5. An electron discharge device as claimed in claim 1 wherein the said further electrode is a frame screen grid having the side rods positioned in the said insulators, the control grid having side rod supporting means at the end of the grid winding opposite said strut projecting beyond the planes of the grid wires, and the screen grid having wires and being positioned so that the wires of the screen grid are closer to those of the control grid than the distance the side rod supporting means of the control grid at the said opposite end project beyond the control grid wires.

6. An electron discharge tube as claimed in claim 5 wherein the screen grid has side rods supporting means adjacent said opposite end of said control grid including a ribbon-shaped strap bent away from the screen grid side rods to allow clearance for the projecting side rod supporting means of the control grid.

7. An electron discharge tube as claimed in claim 6 wherein screen grid side rod supporting means are provided adjacent said one end of said control grid in the form of a U-shaped strap on the outside of the screen grid rods, the ends of the side members of the U abut against the apertured insulator and the space in between the side members of the U is out of contact with the insulator.

References Cited by the Examiner UNITED STATES PATENTS 2,782,338 2/1957 Rhyne 3l3-261 X 2,945,152 7/1960 Marx 313261 X 2,960,621 11/1960 Lane 313350 3,081,800 3/1963 Crosby et a1.

3,126,496 3/1964 Reid 313348 FOREIGN PATENTS 1,001,424 1/1957 Germany.

JOHN W. HUCKERT, Primary Examiner. DAVID J. GALVIN, Examiner. 

1. AN ELECTRON DISCHARGE TUBE HAVING A CATHODE, A FRAME CONTROL GRID SURROUNDING THE CATHODE AND AT LEAST ONE FURTHER ELECTRODE SURROUNDING THE CONTROL GRID, THE CONTROL GRID HAVING A PAIR OF SIDE RODS, THE ENDS OF SAID RODS EXTENDING BEYOND THE END OF SAID CATHODE, A WINDING OF FINE WIRE, UNDER TENSION, WOUND ABOUT THE SIDE RODS IN TWO PLANES EXTENDING BETWEEN AND ALONG SAID RODS AND SPACING MEANS FOR THE SIDE RODS AT EACH END OF THE WINDING; AND AN INSULATOR AT EACH END OF THE GRID WINDING PROVIDING MEANS FOR LOCATING THE CATHODE, THE CONTROL GRID AND THE FURTHER ELECTRODE WITH RESPECT TO ONE ANOTHER; WHEREIN, AT ONE END OF THE CONTROL GRID, THE SIDE ROD SPACING MEANS INCLUDES A STRAIGHT FLAT RIBBON-SHAPED STRUT, SAID STRUT BEING POSITIONED BETWEEN SAID END OF SAID CATHODE AND SAID ENDS OF SAID RODS AND OF THICKNESS NOT GREATER THAN THAT OF THE CATHODE, THE ENTIRE STRUT EXTENDING STRAIGHT ACROSS 